On 25 March 1935, the Physical Review received a paper from Albert Einstein, Boris Podolsky, and Nathan Rosen, with the title “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?” A few days later, on 30 March 1935, I was born. My life with Einstein was off to a promising start. Some would call it an inauspicious start. Abraham Pais, for example, says in his otherwise admirable biography of Einstein [1] that “the only part of this article that will ultimately survive, I believe, is this last phrase [ No reasonable definition of reality could be expected to permit this ], which so poignantly summarizes Einstein's views on quantum mechanics in his later years.” But today, in this centenary of the Einstein annus mirabilis, as the EPR paper and I both turn 70, it is, in fact, the most cited of all Einstein's papers [2]. The debate over its conceptual implications rages hotter than ever, and for the first time, practical (well, for the moment still gedanken practical) applications of the EPR effect have emerged in cryptography and in other areas of quantum information processing. Being only five weeks old, I was unprepared to pay attention to the article that appeared in the New York Times on 4 May 1935 under an elaborate set of headlines and subheads: And I was completely oblivious to the stern rebuke from Einstein himself, published three days later in the Times , which declared that “any information upon which the article … is based was given to you without my authority. It is my invariable practice to discuss scientific matters only in the appropriate forum and I deprecate advance publication of any announcement in regard to such matters in the secular press.” Apparently Podolsky had tipped off the Times to the article, which did not appear in the sacred press until the 15 May issue of Physical Review. It is not clear that Einstein ever forgave him, and I wish I had been old enough to send Podolsky a cross letter myself. Anyone growing up in America in the 1940s knew that the preeminent genius of our age, and perhaps of any other, lived in Princeton, New Jersey, had a predilection for baggy sweaters, and was always badly in need of a haircut—as far ahead of his time in dress and grooming as he was ahead in science during his 1905 annus mirabilis.
On 25 March 1935, the Physical Review received a paper from Albert Einstein, Boris Podolsky, and Nathan Rosen, with the title “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?” A few days later, on 30 March 1935, I was born. My life with Einstein was off to a promising start. Some would call it an inauspicious start. Abraham Pais, for example, says in his otherwise admirable biography of Einstein [1] that “the only part of this article that will ultimately survive, I believe, is this last phrase [ No reasonable definition of reality could be expected to permit this ], which so poignantly summarizes Einstein's views on quantum mechanics in his later years.” But today, in this centenary of the Einstein annus mirabilis, as the EPR paper and I both turn 70, it is, in fact, the most cited of all Einstein's papers [2]. The debate over its conceptual implications rages hotter than ever, and for the first time, practical (well, for the moment still gedanken practical) applications of the EPR effect have emerged in cryptography and in other areas of quantum information processing. Being only five weeks old, I was unprepared to pay attention to the article that appeared in the New York Times on 4 May 1935 under an elaborate set of headlines and subheads: And I was completely oblivious to the stern rebuke from Einstein himself, published three days later in the Times , which declared that “any information upon which the article … is based was given to you without my authority. It is my invariable practice to discuss scientific matters only in the appropriate forum and I deprecate advance publication of any announcement in regard to such matters in the secular press.” Apparently Podolsky had tipped off the Times to the article, which did not appear in the sacred press until the 15 May issue of Physical Review. It is not clear that Einstein ever forgave him, and I wish I had been old enough to send Podolsky a cross letter myself. Anyone growing up in America in the 1940s knew that the preeminent genius of our age, and perhaps of any other, lived in Princeton, New Jersey, had a predilection for baggy sweaters, and was always badly in need of a haircut—as far ahead of his time in dress and grooming as he was ahead in science during his 1905 annus mirabilis.
More than 70 years after its publication, the article by Einstein, Podolsky, and Rosen (EPR) [88] is still cited hundreds of times every year in the literature; this is a very exceptional case of longevity for a scientific article! There is some irony in this situation since, for a long time, the majority of physicists did not pay much attention to the EPR reasoning. They considered it as historically interesting, but with no precise relevance to modern quantum mechanics; the argument was even sometimes completely misinterpreted. Astriking example is given in the Einstein-Born correspondence [89] where Born, even in comments that he wrote after Einstein's death, clearly shows that he never completely understood the nature of the objections raised by EPR. Born went on thinking that the point of Einstein was a stubborn rejection of indeterminism (“look, Albert, indeterminism is not so bad!”), while actually the major concern of EPR was locality and/or separability (we come back later to these terms, which are related to the notion of space-time). If giants like Born could be misled in this way, no surprise that, later on, many others made similar mistakes! This is why, in what follows, we will take an approach that may look elementary, but at least has the advantage of putting the emphasis on the logical structure of the arguments and their generality. Doing so, we will closely follow neither the historical development of the ideas nor the formulation of the original article, but rather will emphasize the generality of the EPR reasoning.
On 25 March 1935 John Tate, the then editor of Physical Review , received a paper that Einstein had co-authored with Boris Podolsky and Nathan Rosen, his younger colleagues at Princeton. The logbooks of Physical Review show that the EPR paper, as it has since become known, bypassed the refereeing process and went straight to press. Four printed pages of beautifully constructed argument appeared in the 15 May issue. They were heralded by a brief article in the New York Times titled "Einstein attacks quantum theory". And so he did.
In 1935, Albert Einstein, Boris Podolsky and Nathan Rosen (EPR) published a thought experiment that is entirely correct, has been demonstrated in real experiments, and is now the most famous in quantum physics. Their pioneering work described, for the first time, quantum correlations and can be regarded as a very early glimpse into today's 'deep' quantum technologies, by which I mean those that enhance functionality by making use of quantum correlations. However, their work also contains a paradox that Erwin Schroedinger had already recognised as such in 1935 and which has since been cemented by the so-called Bell experiments. Here, I am now able to pinpoint the origin of the paradox within the chain of reasoning, which ultimately resolves the paradox.
In the preceding Papers I and II of this series, we have presented a review and upgrade of basic mathematical, physical and chemical methods, and provided a confirmation of the apparent proof of the EPR argument [1] that extended particles within physical media (interior dynamical problems) admit classical counterparts [9], while Einstein’s determinism appears to be progressively verified with the increase of the density of the medium [10]. In this third and final paper of the series, we shown that the EPT argument in general, and Einstein’s determinism in particular, appear to be progressively verified in the structure of mesons, baryon, nuclei, and molecular bonds while being fully verified at the limit of gravitational collapse. We additionally show, apparently for the first time, the validity of the EPR final statement to the effect that the wavefunction [of quantum mechanics] does not provide a complete description of the physical reality” since the covering isowavefunctions of hadronic mechanics provide an otherwise impossible representation of all characteristics of various physical and chemical interior systems existing in nature.
The famously controversial 1935 paper by Einstein, Podolsky, and Rosen (EPR) took aim at the heart of the flourishing field of quantum mechanics. The paper provoked responses from the leading theoretical physicists of the day, and brought entanglement and nonlocality to the forefront of discussion. This book looks back at the seminal year in which the EPR paper was published and explores the intense debate it unleashed. These conversations in print and in private correspondence offer significant insight into the minds of pioneering quantum physicists including Niels Bohr, Erwin Schrödinger and Albert Einstein himself. Offering the most complete collection of sources to date – many published or translated here for the first time – this text brings a rich new context to this pivotal moment in physics history. Both researchers and students in the history and philosophy of science, and enthusiasts alike, will find this book illuminating.
How it all began In 1935, a decade after the invention of quantum theory by Heisenberg (1925) and Schrödinger (1926), three papers appeared, setting the stage for a new concept, quantum entanglement. The previous decade had already seen momentous discussions on the meaning of the new theory, for example by Niels Bohr (see his contribution to Albert Einstein: Philosopher-Scientist in Further reading); but these new papers opened up the gates for a new, very deep philosophical debate about the nature of reality, about the role of knowledge, and about their relation. Since the 1970s, it has become possible for experimenters to observe entanglement directly in the laboratory and thus test the counter-intuitive predictions of quantum mechanics whose confirmation today is beyond reasonable doubt. Since the 1990s, the conceptual and experimental developments have led to new concepts in information technology, including such topics as quantum cryptography, quantum teleportation, and quantum computation, in which entanglement plays a key role. In the first of the three papers, Einstein, Podolsky, and Rosen (EPR) realized that, if two particles had interacted in their past, their properties will remain connected in the future in a novel way, namely, observation on one determines the quantum state of the other, no matter how far away. Their conclusion was that quantum mechanics is incomplete and they expressed their belief that a more complete theory may be found. Niels Bohr replied that the two systems may never be considered independent of each other, and observation on one changes the possible predictions on the other. Finally, Erwin Schrödinger, in the paper which also proposed his famous cat paradox, coined the term “entanglement” (in German Verschränkung ) for the new situation and he called it “not one, but the essential trait of the new theory, the one which forces a complete departure from all classical concepts.”